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Z. Geomorph. N. F., Vol. 25(1981), 1-16

ICE EFFECT ON EROSION AND SEDIMENTATION ON THE ONTARIO SHORES OF JAMES BAY, CANADA

I. PETER MARTINI

University of Guelph, Ontario, Canada

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image_20.jpg (634963 ×Ö½Ú)James Bay is a cold, brackish, inland sea covered for approximately six months of the year by sea ice. Although occasional storm surges occur, it is normally a low energy, shallow (offshore slope 0.5-1.0 m/km), tidal coast. During break-up and at times in summer when pack ice is piled against the shore by wind, the coast is criss-crossed by gouges, and accumulates ice rafted materials. Many of these features remain visible at river mouths, and or near promotories where rates of deposition are low. They disappear during summer from tidal flats, where scattered boulders and patches of unsorted gravel and coarse sand testify to previous ice action. Several types of beam ridges are common along this coast, and they are scoured by ice, and receive considerable amount of ice rafted material. This material is reworked by storm waves, and the legacy of ice action is seldom recognizable, except for rare basal cut and fills.
   The freezing of ice blocks to the ground is another significant sea ice process. When the blocks are lifted during spring tides they remove clumps of vegetation and sediments from lower marshes. This, plus semi-circular depositional features formed around melting ice blocks, generates a pattern of highs and lows whim is rapidly stabilized by vegetation on this fast emerging coast, and is preserved as a slightly modified form in the patterns of pools of upper marshes and fens.
    An indirect effect of sea ice is the mange it creates in longshore and tidal currents, creating ice-walled channels and bays. Parts of the sand flats are eroded by canalized tidal currents, and the infauna population destroyed. A drastic geomorphologic effect is the annual blocking of the shallow Akimiski Strait to the north. For several weeks it becomes an ice-walled bay open to the south and experiencing large tides and tidal currents. Its northwestern coast acquires unique characteristics sum as steep narrow tidal flats, and marshes with long 'U' shaped channels flushed by high tides.

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